1. Field of the Invention
This invention relates to systems and methods for extracting hydrocarbons from a mixture that includes solids and water. More particularly, the invention relates to a system and method for extracting bitumen from a hydro-transport slurry created to facilitate movement of bitumen contained in oil sands from a mining site to a processing site.
2. Description of the Related Art
Oil sands, also referred to as tar sands or bituminous sands, are a combination of solids (generally mineral components such as clay, silt and sand), water, and bitumen. Although the term “sand” is commonly used to refer to the mineral components of the mixture, it is well known that this term is meant to include various other components such as clay and silts. Technically speaking, the bitumen is neither oil nor tar, but a semisolid form of oil which will not flow toward producing wells under normal conditions, making it difficult and expensive to produce. Oil sands are mined to extract the oil-like bitumen which is processed further at specialized refineries. Conventional oil is extracted by drilling traditional wells into the ground whereas oil sand deposits are mined using strip mining techniques or persuaded to flow into producing wells by techniques such as steam assisted gravity drainage (SAGD) or cyclic steam stimulation (CSS) which reduce the bitumen's viscosity with steam and/or solvents.
Various methods and equipment have been developed over many years for mining oil sands and for extracting desired hydrocarbon content from the mined solids.
Conventional oil sand extraction processes involve the following steps:
a) Excavation of the oil sand from a mine face as a volume of ore material. Generally, this is done using conventional strip mining techniques and equipment.
b) Comminution of the ore material to reduce it to conveyable size for conveying from the mine face.
c) Combining the comminuted material with water to form a slurry. Generally, the slurry is formed with hot water, and, optionally other additives.
d) Pumping the slurry to a primary separation facility to separate the mineral from the hydrocarbon components. The pumping step is generally referred to as a “hydro-transport” process. During the slurry formation and hydro-transport process, large constituents in the ore material are further reduced in size, or ablated, and the process of bitumen separation from the solid mineral components is commenced. These effects are referred to as “conditioning” of the slurry.
e) Separating the bulk of the hydrocarbon (i.e. bitumen) content from the mineral component in one or more “primary separation vessels” (PSV) wherein the bitumen portion is entrained in a froth that is drawn off from the surface of the slurry while a significant portion of the mineral is removed as a solids or tailings stream.
f) Hydraulic transport of the tailings to a designated tailings disposal site.
g) Recovery and recycling of clarified water back to the process when released from the tailings slurry within the tailings disposal site.
The above separation and froth concentration steps constitute initial primary extraction of the oil sands to separate the bitumen from the mineral component. The bitumen froth that results after application of the above steps is then delivered to secondary treatment steps that further concentrate and upgrade the bitumen to produce a suitable feed for upgrading to synthetic crude oil or for refining into petroleum products.
Various other intervening steps are also known in the primary extraction process such as withdrawal of a middlings layer from the PSV and oil recovery from tailings by cyclones and flotation to further increase the yield of bitumen from the ore material.
As will be known to persons skilled in the art, the large-scale nature of oil sands mining requires processing facilities of an immense size. As such, these facilities are generally fixed in position. For this reason, transport of the ore material between the various above-mentioned steps generally involves the use of trucks, conveyors, or pipelines or various other known equipment. However, as operations continue, it will be appreciated that the mine face normally recedes further away from the permanent facilities. This, therefore, increases the transport distances and time resulting in increased operating and maintenance costs and environmental impact.
There exists therefore a need to increase the efficiency of at least the transport and primary extraction processes to reduce operating costs. One suggestion that has been proposed is for having one or more of the excavating equipment to be mobile so as to follow the receding mine face. An example of this method is taught in Canadian application number 2,453,697, wherein the excavating and crushing equipment is made mobile so as to advance along with the mine face. The crushed ore is then deposited onto a conveyor, which then transports the ore to a separation facility. This reference also teaches that the conveyor and separation facility can periodically be relocated to a different site once the mine face advances a sufficient distance. However, such relocation, particularly of the separation facility including large gravity separation vessels would involve considerable time, expense and lost production.
Another problem faced with respect to oil sand mining involves the fact that sand constitutes the primary weight fraction of the mineral component of the mined ore material. Thus, it is desirable to separate the minerals as soon as possible “upstream” so as to minimize transport costs. In addition, the transport of mineral components results in considerable wear on the transport mechanisms, which further increases operating and maintenance costs. As well, long hydro-transport distances can over condition the oil sand causing bitumen recoveries to decline as the distances increase. At the same time, separation of the bitumen and mineral components must be done in such a way as to maximize bitumen yield from the ore material.
Thus, there exists a need for an efficient primary extraction process to separate bitumen from the mineral components, preferably in proximity to the mine face to reduce transport costs. The present invention seeks to alleviate at least some of the problems associated with the prior art by providing a novel system and method for extracting the bitumen from a hydro-transport slurry to create an intermediate bitumen froth suitable for further processing. The system of the present invention is preferably mobile so that the primary extraction process can move with the mine face, however, it is also contemplated that the system can be retrofitted to existing fixed primary treatment facilities to improve the operational efficiency of such fixed facilities.